Inter-prediction method and video encoding/decoding method using the inter-prediction method

ABSTRACT

An inter-prediction method and a video encoding/decoding method using the inter-prediction method are disclosed. The video encoding method using inter-prediction includes: encoding a first picture that serves as a reference for random access; inter-prediction encoding a block included in a second picture, which is displayed before the first picture, by using a plurality of reference pictures; generating reference picture information representing whether a past picture, which is displayed before the second picture, is used as a reference picture for encoding the second picture; and transmitting the encoded first and second pictures and the reference picture information.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of Korean Patent Application No.10-2010-0035222, filed on Apr. 16, 2010 and Korean Patent ApplicationNo. 10-2010-0129059, filed on Dec. 16, 2010 in the KIPO (KoreanIntellectual Property Office). Further, this application is the NationalPhase application of International Application No. PCT/KR2011/002545filed Apr. 12, 2011, which designates the United States and waspublished in Korean.

TECHNICAL FIELD

The present disclosure relates to a video encoding/decoding apparatusand method. More particularly, the present disclosure relates to aninter-prediction method, which is capable of preventing a reduction inencoding efficiency during the use of IDR picture for random access, andvideo encoding/decoding technology using the inter-prediction method.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

H.264/AVC uses Instantaneous Decoding Refresh (IDR) picture for enablingan encoded bitstream to be randomly decoded from a specific timeposition. As illustrated in FIG. 1, an encoder deletes decoded picturesfrom a Decoded Picture Buffer (DPB) and clears the DPB immediatelybefore encoding IDR picture. As in the case of the encoder, a decoderalso clears a DPB immediately before decoding IDR picture.

Pictures to be encoded or decoded after the IDR picture of FIG. 1 areencoded with reference to the IDR picture and pictures encoded anddecoded after the IDR picture.

An IDR picture encoding method is substantially identical to an Ipicture encoding method. However, the IDR picture encoding methodsupports a random access function that enables a decoding process to beperformed from a random IDR picture time point by inserting IDR picture.

When encoding inter-pictures, H.264/AVC predicts current picture byusing pictures previously encoded and decoded. As illustrated in FIG. 2,in the case of P picture, a motion estimation is performed by using apast picture existing prior to current picture on the basis of displayorder. A residue signal between a current block and a block determinedthrough the motion estimation is encoded.

As illustrated in FIG. 3, in the case of B picture, a motion estimationis performed by using past picture existing prior to current picture andfuture picture existing after the current picture on the basis ofdisplay order. Then, a residue signal between a current block and ablock determined through the motion estimation is encoded.

According to the H.264/AVC standard, one or more sheets of referencepictures can be used for inter-picture estimation with respect to eachprediction direction. Due to this function, H.264/AVC exhibits superiorcompression performance to other picture compression standards.

H.264/AVC uses IDR picture for supporting a random access function. Asillustrated in FIG. 4, an encoder and a decoder clears a DPB immediatelybefore encoding and decoding IDR picture. Hence, with respect to some ofB pictures displayed before the IDR picture, bidirectional motionestimation cannot be performed during encoding, and therefore, onlyunidirectional motion estimation is performed. Consequently, theencoding efficiency of pictures performing only the unidirectionalmotion estimation is reduced.

In addition, as illustrated in FIG. 5, specific P pictures displayedafter the IDR picture can use only one IDR picture for the referencepicture, but cannot use a plurality of pictures prior to the IDR picturefor the reference picture. Therefore, the encoding efficiency of the Ppicture may be reduced.

DISCLOSURE Technical Problem

Therefore, to solve the above-mentioned problems, the present disclosureseeks to provide an inter-prediction method, which is capable of solvingthe problems of conventional IDR picture used for supporting a randomaccess and improving the encoding and decoding efficiencies, and a videoencoding/decoding method using the inter-prediction method.

SUMMARY

An embodiment of the present disclosure provides a video encoding methodusing inter-prediction, including: encoding a first picture that servesas a reference for random access; inter-prediction encoding a blockincluded in a second picture, which is displayed before the firstpicture, by using a plurality of reference pictures; generatingreference picture information representing whether a past picture, whichis displayed before the second picture, is used as a reference picturefor encoding the second picture; and transmitting the encoded first andsecond pictures and the reference picture information. When a pastreference picture is used for encoding the second picture, the referencepicture information may be information representing the past referencepicture. When a past reference picture is used for encoding the secondpicture, an encoder may encode at least the second picture, and deletereference pictures encoded after the encoding of the first picture,again decoded and stored in a memory.

When encoding the second picture displayed before or after the firstpicture, in the case where past pictures prior to the current secondpicture are stored in a memory storing reference pictures, the storedpast pictures may be copied to a memory storing future referencepictures of the current second picture and be used as future referencepictures. A current second picture may be encoded by using pictures of afuture reference picture memory as well as pictures of a past referencepicture memory. In the case where future pictures after a current secondpicture are stored in a memory storing reference pictures, the storedfuture reference pictures may be copied to a memory storing pastreference pictures of the current second picture and be used as pastreference pictures of the current second picture. A current secondpicture may be encoded by using pictures of a future reference picturememory as well as pictures of a past reference picture memory. The firstpicture may be R picture corresponding to IDR picture, and the secondpicture may be B picture or P picture. The terms “IDR picture” and “Rpicture” in this present disclosure are named for convenience and may bereferred to by other names.

Another embodiment of the present disclosure provides a video encodingmethod using inter-prediction, including: encoding a first picture thatserves as a reference for random access; and inter-prediction encoding ablock included in a second picture, which is displayed before the firstpicture, by using a plurality of reference pictures, wherein theinter-prediction encoding of the block included in the second pictureuses one or more pictures, which are obtained by modifying a decodedfirst picture obtained by decoding the encoded first picture, asreference pictures. The video encoding method may further include:generating modification identification information representing amodification type of the decoded first picture; and transmitting theencoded first and second pictures and the modification identificationinformation to a decoder. The first picture may be R picturecorresponding to IDR picture, and the second picture may be B picture.

Yet another embodiment of the present disclosure provides a videodecoding method using inter-prediction, including: decoding a firstpicture that serves as a reference for random access; andinter-prediction decoding a block included in a second picture, which isdisplayed before the first picture, by using a plurality of referencepictures, wherein the decoding of the block included in the secondpicture is performed based on reference picture information representingwhether a past picture displayed before the second picture is used as areference picture for encoding the second picture. When a past referencepicture is used for decoding the second picture, the reference pictureinformation may be information representing the past reference picture,and when a past reference picture is used for decoding the secondpicture, a decoder may decode at least the second picture, and deletereference pictures decoded prior to the decoding of the first pictureand stored in a memory.

When decoding the second picture displayed before or after the firstpicture, in the case where past pictures before a current second pictureare stored in a memory storing reference pictures, the stored pastpictures may be copied to a memory storing future reference pictures ofthe current second picture and be used as future reference pictures. Acurrent second picture may be decoded by using pictures of a futurereference picture memory as well as pictures of a past reference picturememory. When future pictures after a current second picture are storedin a memory storing reference pictures, stored future reference picturesmay be copied to a memory storing past reference pictures of the currentsecond picture and be used as past reference pictures of the currentsecond picture. A current second picture may be decoded by usingpictures of a future reference picture memory as well as pictures of apast reference picture memory. The first picture may be R picturecorresponding to IDR picture, and the second picture may be B picture.

Yet another embodiment of the present disclosure provides a videodecoding method using inter-prediction, including: decoding a firstpicture that serves as a reference for random access; andinter-prediction decoding a block included in a second picture, which isdisplayed before the first picture, by using a plurality of referencepictures, wherein in the decoding of the block included in the secondpicture, the decoded first picture is modified based on modificationidentification information representing a modification type of thedecoded first picture, and the modified picture is used as a referencepicture. The first picture may be R picture corresponding to IDRpicture, and the second picture may be B picture.

Yet another embodiment of the present disclosure provides aninter-prediction method for video encoding or decoding, including:encoding or decoding a first picture that serves as a reference forrandom access; and inter-prediction encoding or decoding a blockincluded in a second picture, which is displayed before the firstpicture, by using a plurality of reference pictures, wherein in theinter-prediction encoding or decoding of the block included in thesecond picture, the encoded and decoded picture or a picture obtained bymodifying the decoded first picture is used as a reference picture. Thefirst picture may be R picture corresponding to IDR picture, and thesecond picture may be B picture.

Yet another embodiment of the present disclosure provides aninter-prediction method for video encoding or decoding, including:encoding or decoding a first picture that serves as a reference forrandom access; inter-prediction encoding or decoding a block included ina second picture, which is displayed before the first picture, by usinga plurality of reference pictures; and in the case where a pastreference picture is used for encoding or decoding the second picture,after the encoding or decoding of the second picture is completed,deleting reference pictures encoded prior to the encoding of the firstpicture, again decoded and stored in a memory, or reference picturesdecoded prior to the decoding of the first picture and stored in amemory.

When encoding or decoding a second picture displayed before or after thefirst picture, in the case where past pictures before a current secondpicture are stored in a memory storing reference pictures, the storedpast pictures may be copied to a memory storing future referencepictures of the second picture and be used as future reference pictures.When future pictures after a current second picture are stored in amemory storing reference pictures, the stored future pictures may becopied to a memory storing past reference pictures of the current secondpicture and be used as past reference pictures. The first picture may beR picture corresponding to IDR picture, and the second picture may be Ppicture or B picture.

Yet another embodiment of the present disclosure provides aninter-prediction method for video encoding or decoding, including:encoding or decoding a first picture used as a reference picture;inter-prediction encoding or decoding a block included in a secondpicture, which is encoded or decoded after the first picture, by using aplurality of reference pictures; and when past and future referencepictures are used for encoding the second picture and past or futurereference pictures do not exist, copying or modifying the first pictureand using the copied or modified first picture as non-existing past orfuture reference pictures. The first picture may be a picture used as areference picture of an inter-picture, and the second picture may be Bpicture or P picture.

Advantageous Effects

According to the present disclosure as described above, by resetting aDPB immediately before encoding IDR picture, P or B picture after theIDR picture is encoded by using the IDR picture and picturesreconstructed after the IDR picture, without referring to picturesreconstructed before the IDR picture. Therefore, it is possible to solveproblems that reduce the encoding efficiency because a smaller number ofreference pictures are used as compared to P or B pictures encodedbefore the IDR picture.

In addition, according to the present disclosure as described above,when the number of reference pictures of specific P or B picture islimited or smaller than the number reference pictures of other P or Bpictures, a plurality of reference pictures are additionally provided bycopying usable reference pictures and using an arbitrary pictureprocessing method, thereby improving the encoding efficiency.

Moreover, according to the present disclosure as described above, newreference picture generating step and method introduce new syntaxelements or equally operate an encoder or a decoder in accordance with apredefined algorithm. Since the encoder and the decoder generate thesame reference pictures, the quality of reconstructed pictures generatedby the encoder is equal to the quality of decoded pictures generated bythe decoder.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram explaining conventional DPB management where pastpictures before current picture are used for reference picture;

FIG. 2 is a diagram explaining a P picture prediction method;

FIG. 3 is a diagram explaining a B picture prediction method;

FIG. 4 is a diagram explaining problems of B picture encoding whenconventional IDR picture is used;

FIG. 5 is a diagram explaining problems of P picture encoding whenconventional IDR picture is used;

FIG. 6 is a diagram illustrating an example of an H.264 encoder anddecoder;

FIG. 7 is a diagram explaining an MI block prediction method accordingto an embodiment of the present disclosure;

FIG. 8 is a diagram explaining an R picture function and defining termsof pictures according to an embodiment of the present disclosure;

FIG. 9 is a flow chart illustrating a video encoding method usinginter-prediction according to a first embodiment of the presentdisclosure;

FIG. 10 is a flow chart illustrating a video encoding method usinginter-prediction according to a second embodiment of the presentdisclosure;

FIG. 11 is a flow chart illustrating a video decoding method usinginter-prediction according to a third embodiment of the presentdisclosure;

FIG. 12 is a flow chart illustrating a video decoding method usinginter-prediction according to a fourth embodiment of the presentdisclosure;

FIG. 13 is a flow chart illustrating an inter-prediction methodaccording to a fifth embodiment of the present disclosure;

FIG. 14 is a flow chart illustrating an inter-prediction methodaccording to a sixth embodiment of the present disclosure;

FIG. 15 is a flow chart illustrating an inter-prediction methodaccording to a seventh embodiment of the present disclosure;

FIG. 16 is a flow chart illustrating a video encoding method usinginter-prediction according to an eighth embodiment of the presentdisclosure;

FIG. 17 is a flow chart illustrating a video encoding method usinginter-prediction according to a ninth embodiment of the presentdisclosure;

FIG. 18 is a flow chart illustrating a video decoding method usinginter-prediction according to a tenth embodiment of the presentdisclosure;

FIG. 19 is a flow chart illustrating a video decoding method usinginter-prediction according to an eleventh embodiment of the presentdisclosure;

FIG. 20 is a flow chart illustrating an inter-prediction methodaccording to a twelfth embodiment of the present disclosure;

FIG. 21 is a flow chart illustrating an inter-prediction methodaccording to a thirteenth embodiment of the present disclosure;

FIG. 22 is a diagram explaining a first example of a syntax combinationaccording to an embodiment of the present disclosure;

FIG. 23 is a diagram explaining a second example of a syntax combinationaccording to an embodiment of the present disclosure;

FIG. 24 is a diagram explaining a third example of a syntax combinationaccording to an embodiment of the present disclosure;

FIG. 25 is a diagram explaining a fourth example of a syntax combinationaccording to an embodiment of the present disclosure;

FIG. 26 is a diagram explaining a sixth example of a syntax combinationaccording to an embodiment of the present disclosure; and

FIG. 27 is a diagram explaining a seventh example of a syntaxcombination according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, certain embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings.

FIG. 6 is a diagram illustrating an example of an H.264 encoder anddecoder.

In a video compression standard such as H.264, pictures may be encodedas any one of I, P and B frames (or pictures). The I frame is encoded byusing only a spatial correlation within a frame being currently encoded,and can be reconstructed (decoded) by using only one frame data in adecoder, without referring to other frames. The P frame is encoded byusing inter-prediction referring to a reconstructed frame among framesexisting in the past on the basis of display order, and a decoder canreconstruct current picture by using previously reconstructed picture.The B frame is encoded through inter-prediction using a forwardreconstructed picture (list0 in H.264) and a backward reconstructedpicture (list1 in H.264), and a decoder can reconstruct current pictureby using the forward and backward reconstructed pictures.

Referring to FIG. 6, a video encoder performs an intra-predictionprocess 300 or an inter-prediction process 302, obtains a residue 304between current frame and predicted picture 303, and generates abitstream 312 by performing an entropy encoding process 310 on aquantized transform coefficient 308 obtained by performing atransform/quantization process 306 on intra or inter mode informationand the residue. The encoded picture is generated as reconstructedpicture 316 by undergoing an inverse quantization/inverse transformprocess 314 and adding to the predicted picture 303, and is stored in amemory buffer (decoded picture buffer (DPB)) 318 so as to be used forreference frame of pictures to be encoded as next P or B picture.

Referring to FIG. 6, a video decoder 400 is a part of the encoder. Thevideo decoder 400 receives a bitstream, generates reconstructed picture316 through the same process as a decoding loop of the encoder, andoutputs the reconstructed picture 316 to a display stage such that auser views the picture. Also, the video decoder 400 stores thereconstructed picture 316 in the DPB 318 so as to be used for referenceframe of pictures to be reconstructed next time.

In order to allow the decoder 400 to randomly access the picture, IDRframe (in the embodiment of the present disclosure, R framecorresponding to the IDR frame) is inserted at regular intervalswhenever the encoder generates the bitstream. The IDR frame isrepresented as nal_unit_type 5 of a network adaptation layer (NAL) unitin the bitstream. Immediately before encoding the IDR frame, the encoderresets the DPB, and performs encoding by using only reconstructedpictures after the IDR frame, without referring to reconstructedpictures before the IDR frame, when encoding P or B frame after the IDRframe. When the encoder resets the DPB in such a manner, the decoderchecks only nal_unit_type of the NAL unit on the bitstream. Whennal_unit_type is the IDR frame, the decoder may reconstruct pictures bystarting decoding from the IDR frame. If the decoder starts decodingfrom the IDR frame appearing in the middle, the decoding is started insuch a state that no reconstructed pictures are stored in the DPB.Therefore, the DPB is reset from the start of encoding upon thegeneration of the IDR frame in consideration of the state of thedecoder.

On the other hand, in the case where the encoding is performed byinserting the IDR frame so as to support the random access function, therandom access is enabled in the decoder. However, as described above,the insertion of the IDR frame degrades the picture quality. The picturequality of the I frame is substantially equal to the picture quality ofthe IDR frame. However, the picture quality in the subsequent frames ischanged due to a difference of reference pictures. The problems causedby the use of the IDR frame may be solved by the following embodiments.

In an embodiment of the present disclosure, instead of the conventionalIDR picture, a new encoding picture type corresponding to the IDRpicture is defined as refresh (R) picture, and technical details areproposed to solve the problems occurring in the conventional H.264/AVC.The R picture is merely the term and symbol for describing the contentsof the present disclosure, and does not limit the technical contents ofthe present disclosure.

The R picture is a picture type for supporting random access and is areference picture for random access. That is, an encoder or a decodermay perform encoding or decoding from arbitrary R picture. To this end,as in the case of the conventional I picture or IDR picture, blocksconstituting the R picture are generally encoded or decoded by usingonly intra-prediction, without using inter-prediction referring to otherpictures. Alternatively, in order to increase the encoding efficiency, amoving intra (MI) block may be used as illustrated in FIG. 7.

The MI block searches blocks similar to a current block within a singlepicture or slice, represents position information by using a motionvector, transmits the position information, and transmits pixels of eachblock subtracted using Equation 1 below.

In this case, there is no limitation in using the decoded blocks asreference blocks by applying a specific interpolation filter within thecurrent picture or slice so as to search the optimal block.r _(MI) =C _(MI) −R _(MI)  Equation 1

In Equation 1 above, CMI and RMI represent a pixel value of the currentblock and a pixel value of the reference block, respectively, and rMIrepresents a residue value obtained by subtraction of the pixel valuesof the two blocks. The residue signal is transmitted through a transformand quantization process. The description related to FIG. 7 is merely anexemplary embodiment for encoding the R picture. An I picture encodingmethod in the conventional H.264/AVC may be used. In this presentdisclosure, there is no limitation to an R picture encoding method.

The R picture proposed in the embodiment of the present disclosureefficiently manages a reference picture list, increases the encodingefficiency of pictures adjacent to the R picture in display order, andsupports a random access function. In order to efficiently explain the Rpicture function, the terms of pictures influencing the encodingefficiency due to the use of the R picture are summarized as illustratedin FIG. 8.

In FIG. 8, B pictures existing among past P, I or R pictures closest tothe current R picture in display order are defined BP, and B or Ppictures existing after the R picture in display order and using thedecoded current R picture as the reference picture are defined as BF andPF, respectively.

FIG. 9 is a flow chart illustrating a video encoding method usinginter-prediction according to a first embodiment of the presentdisclosure.

Referring to FIG. 9, R picture as a first picture, which serves as areference for random access, is encoded (S910). A block included in Bpicture (for example, BP picture of FIG. 8) as a second picture, whichis displayed before the R picture, is inter-prediction encoded by usinga plurality of reference pictures (S930).

In addition, reference picture information is generated (S950). Thereference picture information (for example, syntax of Table 1)represents whether past picture (for example, modified reference pictureof the decoded R picture of FIG. 15), which is displayed before the Bpicture, is used as the reference picture for encoding the B picture. Instep S930, when the past reference picture is used for encoding the Bpicture, the reference picture information may be informationrepresenting the past reference picture. In addition, in the case ofusing the past reference picture for encoding the B picture, at leastafter the encoding of the B picture, the encoder may delete referencepictures encoded before the encoding of the R picture, again decoded andthen stored in a memory.

Then, as described above, the encoded R picture, the encoded B picture,and the reference picture information are transmitted to the decoder(S970).

FIG. 10 is a flow chart illustrating a video encoding method usinginter-prediction according to a second embodiment of the presentdisclosure.

Referring to FIG. 10, R picture as a first picture, which serves as areference for random access, is encoded (S1010). The encoded R pictureis decoded, and a plurality of pictures obtained by modifying thedecoded R picture is generated as reference picture (S1030).

Then, a block included in B picture (for example, BP picture of FIG. 8)as a second picture, which is displayed before the R picture, isinter-prediction encoded by using a plurality of reference pictures(S1050).

In addition, modification identification information representing a typeof the modified decoded R picture is generated in step S1030. After stepS1050, the encoded R picture, the encoded B picture, and themodification identification information are transmitted to the decoder.Moreover, although not illustrated, information on the reference picturegenerated in step S1030 may be generated in correspondence to theprocesses of steps S950 and S970 of FIG. 9, and the reference pictureinformation may be transmitted to the decoder.

FIG. 11 is a flow chart illustrating a video decoding method usinginter-prediction according to a third embodiment of the presentdisclosure.

Referring to FIG. 11, R picture as a first picture, which serves as areference for random access, is decoded (S1110), and reference pictureinformation received from the encoder is analyzed (S1130).

Then, a block included in B picture (for example, BP picture of FIG. 8)as a second picture, which is displayed before the R picture, isinter-prediction decoded by using a plurality of reference pictures, anda process of decoding the block included in the B picture is performedbased on the reference picture information representing whether pastpicture, which is displayed before the B picture, is used as thereference picture for encoding the B picture (S1150).

FIG. 12 is a flow chart illustrating a video decoding method usinginter-prediction according to a fourth embodiment of the presentdisclosure.

Referring to FIG. 12, R picture as a first picture, which serves as areference for random access, is decoded (S1210), and modificationidentification information representing a modification type of thedecoded R picture is analyzed (S1230).

Then, a plurality of reference pictures are generated by modifying thedecoded R picture according to the analyzed modification identificationinformation (S1250), and a block included in B picture (for example, BPpicture of FIG. 8) as a second picture, which is displayed before the Rpicture, is inter-prediction decoded by using the plurality of referencepictures (S1270).

FIG. 13 is a flow chart illustrating an inter-prediction methodaccording to a fifth embodiment of the present disclosure.

Referring to FIG. 13, R picture as a first picture, which serves as areference for random access, is encoded or decoded (S1310), and aplurality of reference pictures are generated by modifying the decoded Rpicture (the R picture encoded in the encoder and then decoded, or the Rpicture decoded in the decoder) step by step (S1330).

Regarding the process of step S1330, the encoder performs the sameprocess as step S1030 of FIG. 10, and the decoder performs the sameprocess as steps S1230 to S1250.

After encoding or decoding the R picture, a block included in B picture(for example, BP picture of FIG. 8) as a second picture, which isdisplayed before the R picture, is inter-prediction encoded or decodedby using the plurality of reference pictures (S1350).

FIG. 14 is a flow chart illustrating an inter-prediction methodaccording to a sixth embodiment of the present disclosure.

Referring to FIG. 14, R picture as a first picture, which serves as areference for random access, is encoded or decoded (S1410). Afterdecoding the R picture, a block included in B picture (for example, BPpicture of FIG. 8) as a second picture, which is displayed before the Rpicture, is inter-prediction encoded or decoded by using the pluralityof reference pictures (S1430).

Then, in the case of using past reference picture for encoding ordecoding the B picture, after the encoding or decoding of the B pictureis completed, reference pictures encoded before the encoding of the Rpicture, again decoded and then stored in a memory or reference picturesdecoded before the decoding of the R picture and stored in a memory aredeleted (S1450).

FIG. 15 is a flow chart illustrating an inter-prediction methodaccording to a seventh embodiment of the present disclosure.

Referring to FIG. 15, R picture as a first picture, which serves as areference for random access, is encoded or decoded (S1510), and aplurality of reference pictures are generated by modifying the decoded Rpicture (the R picture encoded in the encoder and then decoded, or the Rpicture decoded in the decoder) step by step (S1530).

Regarding the process of step S1530, the encoder performs the sameprocess as step S1030 of FIG. 10, and the decoder performs the sameprocess as steps S1230 to S1250.

After encoding or decoding the R picture, a block included in P picture(for example, PP picture of FIG. 8) as a second picture, which isdisplayed after the R picture, is inter-prediction encoded or decoded byusing at least one of the plurality of reference pictures (S1550).

FIG. 16 is a flow chart illustrating a video encoding method usinginter-prediction according to an eighth embodiment of the presentdisclosure. Referring to FIG. 16, after past reference pictures areselected from a memory (list 0 DPB, L0) storing past reference picturesdisplayed before the current picture, the selected reference picturesare copied to a memory (list 1 DPB, L1) storing future referencepictures displayed after the current picture (S1610). Then, the currentpicture is prediction-encoded by using the reference pictures stored inthe memories L0 and L1 (S1620). In this case, the current picture is Bpicture.

In next step, reference picture information (for example, syntax ofTable 1) used as the reference picture for the encoding of the currentpicture is generated (S1630). In step S1630, either or both of the pastreference picture and the future reference picture may be used for theencoding of the current picture. Then, as described above, the encodedcurrent picture and the reference picture information are transmitted tothe decoder (S1640).

FIG. 17 is a flow chart illustrating a video encoding method usinginter-prediction according to a ninth embodiment of the presentdisclosure. Referring to FIG. 17, after future reference pictures areselected from a memory (list 1 DPB, L1) storing future referencepictures displayed after the current picture, the selected futurereference pictures are copied to a memory (list 0 DPB, L0) storing pastreference pictures displayed before the current picture (S1710). Then,the current picture is prediction-encoded by using the referencepictures stored in the memories L0 and L1 (S1720). In this case, thecurrent picture is B picture.

In next step, reference picture information (for example, syntax ofTable 1) used as the reference picture for the encoding of the currentpicture is generated (S1730). In step S1730, either or both of the pastreference picture and the future reference picture may be used for theencoding of the current picture. Then, as described above, the encodedcurrent picture and the reference picture information are transmitted tothe decoder (S1740).

FIG. 18 is a flow chart illustrating a video decoding method usinginter-prediction according to a tenth embodiment of the presentdisclosure. Referring to FIG. 18, a received signal for current pictureis decoded (S1810), and reference picture information received from anencoder is analyzed. Then, some pictures are selected from a memory(list 0 DPB, L0) storing past reference pictures displayed before thecurrent picture, and the selected reference pictures are copied to amemory (list 1 DPB, L1) storing future reference pictures displayedafter the current picture (S1820). An inter-prediction decoding isperformed by using blocks included in the pictures stored in thememories L0 and L1, based on reference picture information representingwhich picture is used as the reference picture for encoding (S1830).

FIG. 19 is a flow chart illustrating a video decoding method usinginter-prediction according to an eleventh embodiment of the presentdisclosure. Referring to FIG. 19, a received signal for current pictureis decoded (S1910), and reference picture information received from anencoder is analyzed. Then, some pictures are selected from a memory(list 1 DPB, L1) storing future reference pictures displayed after thecurrent picture, and the selected reference pictures are copied to amemory (list 0 DPB, L0) storing past reference pictures displayed beforethe current picture (S1920). An inter-prediction decoding is performedby using blocks included in the pictures stored in the memories L0 andL1, based on reference picture information representing which picture isused as the reference picture for encoding (S1930).

FIG. 20 is a flow chart illustrating an inter-prediction methodaccording to a twelfth embodiment of the present disclosure. Referringto FIG. 20, after past reference pictures are selected from a memory(list 0 DPB, L0) storing past reference pictures displayed before thecurrent picture, the selected reference pictures are copied to a memory(list 1 DPB, L1) for the future reference pictures displayed after thecurrent picture (S2010). Then, the current picture is prediction-encodedand prediction-decoded by using the reference pictures stored in thememories L0 and L1 (S2020). In this case, the current picture is Ppicture or B picture. In step S2020, either or both of the pastreference picture and the future reference picture may be used for theencoding and decoding of the current picture.

FIG. 21 is a flow chart illustrating an inter-prediction methodaccording to a thirteenth embodiment of the present disclosure.Referring to FIG. 21, after future reference pictures are selected froma memory (list 1 DPB, L1) storing future reference pictures displayedafter the current picture, the selected reference pictures are copied toa memory (list 0 DPB, L0) storing past reference pictures displayedbefore the current picture (S2110). Then, the current picture isprediction-encoded and prediction-decoded by using the referencepictures stored in the memories L0 and L1 (S2120). In this case, thecurrent picture is B picture. In step S2120, either or both of the pastreference picture and the future reference picture may be used for theencoding and decoding of the current picture.

Hereinafter, various examples of detailed technologies for implementingthe first to thirteenth embodiments of the present disclosure will bedescribed with reference to FIGS. 22 to 27.

According to the embodiment of the present disclosure, R picture or Rpicture slice header may include a syntax (in this embodiment, referredto as reference picture information and modification identificationinformation) as shown in Table 1 below.

TABLE 1 past_pic_ref_type, if(past_pic_ref_type==1){,  past_L0_R_pic_process_type, }, past_L1_R_pic_process_type,fut_L0_R_pic_process_type,

The function of the syntax of Table 1 will be described below.

1) past_pic_ref_type

past_pic_ref_type is a syntax element that represents whether pastreference picture is used for encoding B_(P) and/or, if used, which pastreference picture is used. A value of past_pic_ref_type may bedetermined in the range of 0 to 2, and the picture affected by the valueof past_pic_ref_type is B_(P). An example of the function of the encoderor the decoder according to the value of past_pic_ref_type determined inthe range of 0 to 2 will be described below.

When the value of past_pic_ref_type is 0, the encoder or the decoderuses (decoded) pictures of time point prior to B_(P), based on displayorder, as past reference picture (List 0 reference picture) of B_(P). Tothis end, when the value of this syntax element is 0, the decoder doesnot delete the already decoded pictures stored in the DPB, butcontinuously stores the decoded pictures until a predetermined timepoint and then deletes the decoded pictures. For example, immediatelyafter decoding all or some of the pictures, whose display order is laterthan the R picture, among the pictures decoded after the R picture,pictures decoded before the R picture and stored in the DPB may bedeleted.

When the value of past_pic_ref_type is 1, the encoder or the decoderdeletes the already decoded pictures stored in the DPB, modifies thedecoded current R picture, and stores the modified R picture in the DPBso as to use the modified R picture as the past reference picture.

When the value of past_pic_ref_type is 2, the encoder or the decoderdeletes the already decoded pictures stored in the DPB. Only pictures(decoded pictures) of time point after BP, based on display order, thatis, only the future reference pictures (List 1 reference pictures) ofBP, are stored in the DPB so as to use the reference pictures as thereference pictures for encoding or decoding B_(P).

2) past_L0_R_pic_process_type

past_L0_R_pic_process_type is a syntax element that is encoded only whenthe value of past_pic_ref_type is 1, and represents a method ofmodifying a decoded current R picture. A value ofpast_L0_R_pic_process_type may be determined in the range of 0 to 3, andthe corresponding picture is B_(P). An example of the function of theencoder or the decoder according to the value ofpast_L0_R_pic_process_type determined in the range of 0 to 3 will bedescribed below.

When the value of past_L0_R_pic_process_type is 0, the encoder or thedecoder applies a low pass filtering (LPF) process to the decodedcurrent R picture step by step and then uses the LPF-processed R pictureas the past reference picture of B_(P).

When the value of past_L0_R_pic_process_type is 1, the encoder or thedecoder applies a zoom-in process to the decoded current R picture stepby step and then uses the zoomed-in R picture as the past referencepicture of B_(P).

When the value of past_L0_R_pic_process_type is 2, the encoder or thedecoder applies a zoom-out process to the decoded current R picture stepby step and then uses the zoomed-out R picture as the past referencepicture of B_(P).

When the value of past_L0_R_pic_process_type is 3, the encoder or thedecoder applies a brightness adjustment process to the decoded current Rpicture step by step and then uses the brightness-adjusted R picture asthe past reference picture of B_(P).

3) past_L1_R_pic_process_type

past_L1_R_pic_process_type is a syntax element that represents futurereference picture used for encoding or decoding BP. A value ofpast_L1_R_pic_process_type may be determined in the range of 0 to 4, andthe corresponding picture is B_(P). An example of the function of theencoder or the decoder according to the value ofpast_L1_R_pic_process_type will be described below.

When the value of past_L1_R_pic_process_type is 0, the encoder or thedecoder uses only the decoded current R picture as the future referencepicture (List 1 reference picture) of B_(P), without modifying the Rpicture.

When the value of past_L1_R_pic_process_type is 1, the encoder or thedecoder uses the decoded current R picture and the pictures, which areobtained by applying the LPF process to the decoded current R picturestep by step, as the future reference picture of B_(P).

When the value of past_L1_R_pic_process_type is 2, the encoder or thedecoder uses the decoded current R picture and the pictures, which areobtained by applying the zoom-in process to the decoded current Rpicture step by step, as the future reference picture of B_(P).

When the value of past_L1_R_pic_process_type is 3, the encoder or thedecoder uses the decoded current R picture and the pictures, which areobtained by applying the zoom-out process to the decoded current Rpicture step by step and, as the future reference picture of B_(P).

When the value of past_L1_R_pic_process_type is 4, the encoder or thedecoder uses the decoded current R picture and the pictures, which areobtained by applying the brightness adjustment process to the decodedcurrent R picture step by step, as the future reference picture ofB_(P).

4) fut_L0_R_pic_process_type

fut_L0_R_pic_process_type is a syntax element that represents pastreference picture used for encoding or decoding B_(F) or P_(F). A valueof fut_L0_R_pic_process_type may be determined in the range of 0 to 4,and the corresponding picture is BF. An example of the function of theencoder or the decoder according to the value offut_L0_R_pic_process_type will be described below.

When the value of fut_L0_R_pic_process_type is 0, the encoder or thedecoder uses only the decoded current R picture as the past referencepicture of BF or PF, without modifying the R picture.

When the value of fut_L0_R_pic_process_type is 1, the encoder or thedecoder uses the decoded current R picture and the pictures, which aremodified by applying the LPF process to the decoded current R picturestep by step, as the past reference picture of B_(F) or P_(F).

When the value of fut_L0_R_pic_process_type is 2, the encoder or thedecoder uses the decoded current R picture and the pictures, which aremodified by applying the zoom-in process to the decoded current Rpicture step by step, as the past reference picture of B_(F) or P_(F).

When the value of fut_L0_R_pic_process_type is 3, the encoder or thedecoder uses the decoded current R picture and the pictures, which aremodified by applying the zoom-out process to the decoded current Rpicture step by step, as the past reference picture of B_(F) or P_(F).

When the value of fut_L0_R_pic_process_type is 4, the encoder or thedecoder uses the decoded current R picture and the pictures, which aremodified by applying the brightness adjustment process to the decodedcurrent R picture step by step, as the past reference picture of B_(F)or P_(F).

Various embodiments, including at least the first to thirteenthembodiments of FIGS. 9 to 21, may be implemented by combinations of theabove-described syntaxes.

As one example of the combinations of the above-described syntaxes, whenthe value of past_pic_ref_type is 0 and the value ofpast_L1_R_pic_process_type is in the range of 1 to 4, B picturesbelonging to BP are encoded or decoded as illustrated in FIG. 22.

As another example of the combinations of the above-described syntaxes,when the value of past_pic_ref_type is 1; the value ofpast_L0_R_pic_process_type is in the range of 0 to 3; and the value ofpast_L1_R_pic_process_type is 0, pictures belonging to BP are encoded ordecoded as illustrated in FIG. 23.

As yet another example of the combinations of the above-describedsyntaxes, when the value of past_pic_ref_type is 2 and the value ofpast_L1_R_pic_process_type is in the range of 1 to 4, B picturesbelonging to B_(P) are encoded or decoded as illustrated in FIG. 24.

As still another example of the combinations of the above-describedsyntaxes, when the value of fut_L0_R_pic_process_type is in the range of1 to 4, B or P pictures belonging to B_(F) or P_(F) are encoded ordecoded as illustrated in FIG. 25.

The LPF process, the zoom-in process, the zoom-out process, and thebrightness adjustment process used in past_L0_R_pic_process_type,past_L1_process_R_pic_type, and fut_L0_R_pic_process_type may be appliedstep by step according to the temporal distance of display order fromthe current picture. As the temporal distance of the display order iscloser, the modification may be performed with a slight level, and asthe temporal distance of the display order is farther, the Rmodification may be performed with a strong level.

In this case, there is no limitation to the strong-level R picturemodification as the distance is closer and the slight-level modificationas the distance is farther, depending on the temporal distance of thedisplay order.

According to the above-described embodiment, the encoder and the decodermanage the memory, that is, the DPB, in the same manner. Therefore, byusing the same reference pictures stored in the DPB, the encoder encodeseach picture and the decoder decodes each picture.

In the above-described embodiment, the encoder selects the values of thesyntax elements, such as past_pic_ref_type, past_L0_R_pic_process_type,past_L1_R_pic_process_type or fut_L0_R_pic_process_type, by using anappropriate method, and inserts the syntax elements to the pictureheader or the slice header of the syntax elements, or other suitablebitstream layer. The decoder parses the syntax elements and performs arelevant operation according to the values of the respective syntaxelements.

In the above-described embodiment, new syntax elements for controllingthe operation of the decoder have been introduced. However, according toanother embodiment of the present disclosure, the above-describedproblem of the conventional IDR picture may be solved in a simplermanner by operating the encoder and the decoder in the same manneraccording to a predefined algorithm, without introduction of the syntaxelement such as past_pic_ref_type. For example, in the above-describedembodiment, various DPB managements can be performed according to thevalue of past_pic_ref_type. In another embodiment, instead oftransmitting past_pic_ref_type, the function corresponding to the casewhere the value of past_pic_ref_type is 0 may be performed in the samemanner by the encoder and the decoder.

In addition, in the embodiment of the present disclosure, although themethod of modifying the decoded R picture is designated according to thevalue of each syntax, the 1:1 correspondence of the value and thecorresponding modifying method may be changed according to a predefinedrule.

The number of steps of modifying all decoded R pictures may bedetermined according to the number of reference pictures set by theuser.

Although the method of modifying all R pictures has been applied inunits of pictures or slices in the embodiments of the presentdisclosure, there is no limitation to applying the method of modifyingthe R picture transmitted from the slice header in units of blocks.

In addition, as illustrated in FIG. 26, when encoding and decoding thecurrent picture B1, a specific frame, all frames or some frames amongthe past reference pictures R, B2, B1, B2 and P may be copied to afuture reference picture buffer, and may be used for prediction encodingand decoding of the current picture B1.

In addition, as illustrated in FIG. 27, when encoding and decoding thecurrent picture B1, a specific frame, all frames or some frames amongthe future reference pictures may be copied to a past reference picturebuffer, and may be used for prediction encoding and decoding of thecurrent picture B1.

According to the embodiment of the present disclosure, in order to usethe decoded pictures existing before the BP pictures (in display order)or the modified decoded current R picture as the reference picture ofthe BP pictures of FIG. 8, the syntax is added to the slice header.However, there is no limitation to encoding the corresponding BPpictures by using only one predefined method.

In addition, when the decoded current R picture is modified and used asthe reference picture of BF and PF pictures, the syntax is added to theslice header in order to encode the modifying method. However, there isno limitation to encoding the BF or PF pictures by using only onepredefined method.

In addition, in the embodiments of the present disclosure, there is nolimitation to a type, size, or order of a filter used for modifying thedecoded R picture.

In addition, in the embodiments of the present disclosure, there is nolimitation to the zoom-in method and the picture/block interpolationmethod, which are used for modifying the decoded R picture.

In addition, in the embodiments of the present disclosure, there is nolimitation to the zoom-out method and the picture/block interpolationand sampling method, which are used for modifying the decoded R picture.

In addition, in the embodiments of the present disclosure, there is nolimitation to the brightness change method and the number of brightnesschange parameters, which are used for modifying the decoded R picture.

Moreover, in the embodiments of the present disclosure, the decodedcurrent R picture is copied or modified so as to be used for thereference pictures of the BF and PF pictures. However, there is nolimitation to the copy or modification of an arbitrary type of thereference picture.

Although exemplary embodiments of the present disclosure have beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from essential characteristics of thedisclosure. Therefore, exemplary aspects of the present disclosure havenot been described for limiting purposes. Accordingly, the scope of thedisclosure is not to be limited by the above aspects but by the claimsand the equivalents thereof.

INDUSTRIAL APPLICABILITY

As described above, the present disclosure is highly useful forapplication in the fields because various embodiments are applied to thevideo encoding/decoding technology to solve the problems during the useof the IDR picture for the random access, thereby improving the encodingand decoding efficiency.

The invention claimed is:
 1. A video encoding method usinginter-prediction, comprising: encoding a first picture, wherein thefirst picture serves as a random access picture and is encoded withoutreferring to a reference picture which has already encoded and thendecoded; inter-prediction encoding a block included in a second picture,which is encoded after the first picture and displayed before the firstpicture, by using a plurality of reference pictures; generatingreference picture information representing whether one or more pastpictures, which are encoded before the first picture and displayedbefore the first picture, are used as reference pictures for encodingthe second picture; and transmitting the encoded first and secondpictures and the reference picture information, wherein, when the one ormore past pictures are used as the reference pictures for encoding thesecond picture, the one or more past pictures are deleted from a memoryafter encoding at least the second picture.
 2. The video encoding methodof claim 1, wherein when the past pictures are used for encoding thesecond picture, the reference picture information is informationrepresenting the past pictures.
 3. The video encoding method of claim 1,wherein when encoding the second picture displayed before the firstpicture, in the case where past pictures prior to the current secondpicture are stored in a memory storing reference pictures, the storedpast pictures are copied to a memory storing future reference picturesof the current second picture and are used as future reference pictures.4. The video encoding method of claim 1, wherein in the case wherefuture pictures after a current second picture are stored in a memorystoring reference pictures, the stored future reference pictures arecopied to a memory storing past pictures of the current second pictureand are used as past reference pictures of the current second picture.5. The video encoding method of claim 1, wherein the first picture is Rpicture corresponding to IDR picture, and the second picture is Bpicture or P picture.
 6. A video decoding method using inter-prediction,comprising: decoding a first picture, wherein the first picture servesas a random access picture and is a picture encoded without referring toa reference picture which has already encoded and then decoded; andinter-prediction decoding a block included in a second picture, which isdecoded after the first picture and displayed before the first picture,by using a plurality of reference pictures, wherein the decoding of theblock included in the second picture is performed based on referencepicture information representing whether one or more past pictures,which are encoded before the first picture and displayed before thefirst picture, are used as reference pictures for encoding the secondpicture, wherein, when the one or more past pictures are used fordecoding the second picture, the one or more past pictures are deletedfrom a memory after decoding at least the second picture.
 7. The videodecoding method of claim 6, wherein when decoding the second picturedisplayed before the first picture, in the case where past picturesbefore a current second picture are stored in a memory storing referencepictures, the stored past pictures are copied to a memory storing futurereference pictures of the current second picture and are used as futurereference pictures.
 8. The video decoding method of claim 6, whereinwhen future pictures after a current second picture are stored in amemory storing reference pictures, and stored future reference picturesare copied to a memory storing past pictures of the current secondpicture and are used as past reference pictures of the current secondpicture.
 9. The video decoding method of claim 6, wherein the firstpicture is R picture corresponding to IDR picture, and the secondpicture is B picture.